The use of color monitors for computers has accelerated the need for color printers that can produce a satisfactory printout corresponding as closely as possible to what is displayed on the screen. With such equipment, determining what constitutes a “satisfactory” color printout is often quite problematic.
Part of this problem arises from the subjective nature of color. Color is a sensation produced by the combined effects of light, objects, and human vision. A particular color or combination of colors may be appealing to one person while at the same time being offensive to another.
Another part of the “satisfactory”-color definitional problem arises from the different color technologies used in computer monitors and color printers. For example, computer monitors are based on a color gamut of red, green and blue pixels (RGB), whereas color printers such as xerographic printers or inkjet printers are typically based on a color gamut of cyan, magenta, yellow and black (CMYK). The RGB color components of computer monitors are combined together in an “additive” way by mixing red, green and blue light rays to form a first variety of different colors; but the CMYK components of color toners or inks are applied to media in different combinations in a “subtractive” way to form a second variety of different colors.
Various different color-management techniques have been used to provide some form of matching between, for instance, the colors viewed on a computer monitor and the colors printed by a specific printer using a given toner set or ink formula on a particular type of printing medium. Such color-management techniques have also employed different types of halftoning algorithms (in this art commonly called “rendition” or sometimes “rendering”) to improve appearance of color printout of various type of objects (or in traditional publications jargon “copy”). Moreover to improve the appearance of the printed image, other techniques or operations have been applied. These color improvement techniques include black overprint, anti-aliasing, and trapping. Black overprint is a color improvement technique that involves printing a black foreground object directly over a non-black background object by adding black colorant over the background object. This technique offers improved tolerance to color plane misregistration compared to the typical technique of knockout. Anti-aliasing is a color improvement operation that involves the use of intermediate levels of intensity to achieve more accurate line work rendition and reduction in the jagged effects. Trapping is a color improvement operation that involves removing defects caused by misregistration between color separations that manifest as gaps and hue shifts in overlaps near the edges of abutting objects of different colors.
Desktop publishing software has created an additional dimension of the satisfactory-color-definition problem by printing together, in a composite document, objects (or “copy”) of different types. Such types include photos and photograph-like images, business graphics (e.g., charts and logos), and scalable text in both color and black.
With the advent of having such diverse objects within a print job, the necessity to have black overprint, anti-aliasing, and trapping available to the digital front end (“DFE”) of the color printing system becomes more essential. Conventionally, these color improvement operations have been applied automatically or by user direction on a whole job basis to improve the quality of the image being produced. However, these color improvement operations have a negative impact with respect to the processing time as well as the processing resources required to decompose each page of the job to perform the desired operations. Since these color improvement operations have a negative processing impact, these color improvement operations are usually only “turned on” on a job basis. This programming on a job basis is still too ineffective when only a few pages of a very large job requires such color improvement operations to actually improve the quality of the printed image. To utilize this extra processing time and resources for pages, whose quality will not be noticeably improved, can have a significant negative impact upon the productivity of the DFE and the overall color printing system.
There is thus a need for a printer-management system that enables a user or operator to take advantage of the color improvement operations discussed above. Such a system must also provide flexibility so that these processing intensive color improvement operations can be applied on a discriminate basis so as to avoid any unneeded negative impact upon productivity. Such a system will apply these color improvement operations where needed and minimize a negative impact upon processing resources.